This kind of head portion protecting air bag apparatus includes, for example, a structure in which an inner tube is internally provided along a gas passage (an inflow portion) of an air bag so as to restrict bag damage by the gas supplied to an air bag from the inflator, as disclosed in Japanese Patent Application Laid-Open No. 11-321536, and a structure in which a tubular body is provided along a gas passage of an air bag so as to restrict bag damage applied by a gas supplied to the air bag from an inflator, for example, as disclosed in Japanese Patent Application Laid-Open Nos. 11-301394 and 2000-127886.
In the conventional head portion protecting air bag apparatus mentioned above, since the inner tube or the tubular body (a protecting member) mentioned above is provided in the gas passage of the air bag so as to restrict the bag damage due to the gas supplied to the air bag from the inflator, there is a risk that the inner tube or the tubular body mentioned above prevents the air bag from being folded so as to make it more difficult to house the air bag in the vehicle and cause a cost increase of the air bag apparatus.
On the contrary, in the air bag apparatus, it is necessary to satisfy various requirements in view of inflating and deploying performance of the air bag (a requirement of making a time after starting inflation and deployment until completing inflation and deployment equal to or less than a set time, a requirement of maintaining an initial internal pressure after starting inflation and deployment until completing inflation and deployment equal to or more than a high set pressure, a requirement of maintaining an internal pressure equal to or more than a low set pressure for a predetermined time after an initial predetermined time has elapsed after completing inflation and deployment, and the like).
In order to reduce the time for completing inflation and deployment of the air bag and increase the initial internal pressure, there is generally employed a countermeasure of increasing a gas supplying capacity of the inflator. However, when increasing the gas supplying capacity of the inflator, the bag damage is increased and it is impossible to increase a time of holding the internal pressure. Accordingly, it is necessary to sufficiently apply a coating for keeping airtightness, for example, onto a surface of the air bag so as to restrict bag damage and increase airtight performance, or it is necessary to increase a gas supply capacity of the inflator in addition to increasing airtight performance of the air bag, and there is a problem that improving the inflating and deploying performance of the air bag and reducing a cost reduction is contradictive. Such a problem can be solved by restricting bag damage of the air bag by a means capable of being realized at a low cost.